With the miniaturization of semiconductor elements, a demand for the deposition characteristics is becoming stricter. A gate insulating film, for example, is required to have a very small thickness. Also, a thin electrode film formed on a very thin insulating film, for example, is required to be stably deposited. Moreover, due to a concern in adverse effects on element performance exerted by impurities such as carbon in each film or at the interface between thin films, a lower impurity level is required.
The sputtering method used as one of deposition methods can deposit a high quality film because it employs a material which contains no impurities such as carbon, unlike the CVD method. The sputtering method is also advantageous in terms of avoiding problems or challenges such as a process of eliminating toxic substances generated by by-products and unused materials as this method employs no toxic organic metal material, unlike the CVD method.
In a sputtering method of depositing a thin film on a substrate such as silicon (to be simply referred to as a “substrate” hereinafter), a target holder in a vacuum chamber evacuated to a vacuum holds a vapor deposition source called a target made of a material to be deposited on a substrate. A substrate holder in the vacuum chamber supports the substrate. A gas such as Ar is introduced into the vacuum chamber, and a high voltage is applied to the target, thereby generating a plasma. In the sputtering method, a target material is deposited on the substrate, supported by the substrate holder, using the phenomenon in which the target is sputtered by charged particles in the discharge plasma. In general, positive ions in the plasma impinge on the target having a negative potential, so atoms and molecules are sputtered from the target material. These atoms and molecules will generically be referred to as sputtered particles hereinafter. These sputtered particles adhere to the substrate to form a film containing the target material on the substrate.
In a sputtering apparatus, a shield plate that can be opened and closed, called a shutter, is normally placed between a target and a substrate. This shutter is used to control the timing of the start of deposition so as not to start a deposition process until the plasma state in the vacuum chamber becomes stable. That is, the shutter is kept closed so as not to deposit a film on the substrate in the period from when a plasma is generated upon application of a high voltage to the target until the plasma becomes stable. After the plasma becomes stable, the shutter opens to start deposition. When the start of deposition is controlled using the shutter in this way, a film can be deposited on the substrate with high controllability using a stable plasma, thus depositing a film with high quality.
A plasma processing apparatus disclosed in PTL1 includes a wafer holder, moving shutter, and shutter accommodation unit disposed in a vacuum chamber. The wafer holder includes a plate on which a wafer is placed, and a plurality of wafer lift pins. The moving shutter moves parallel to the wafer. The shutter accommodation unit accommodates the moving shutter while the wafer is processed by a plasma.